The present invention relates to a semiconductor device and a sensor system and, particularly, to a semiconductor device and a sensor system including an analog front-end circuit.
Sensors are increasingly employed in various equipments such as consumer products, industrial products and medical products because of improvement of usability, enlargement of ecosystem, penetration of health care, enhancement of security and the like. Factors behind this trend include the improved usability of a sensor device and the low voltage and the low power of an analog circuit which is essential to implement a sensor to allow system downsizing and cost reduction. There are various types of sensors including a temperature sensor, infrared sensor, photosensor and shock sensor, and a circuit for processing a sensor signal is formed and characteristic setting is made in accordance with the principle of operation.
In such equipment, a control device such as a microcomputer performs control processing in accordance with a measurement result of a sensor. Because a measurement signal that is output from a sensor cannot be processed by a control device such as a microcomputer, analog front-end processing such as amplification to a specified level and removal of noise is performed by an analog front-end (AFE) circuit before input to the microcomputer. In the analog front-end processing, design in accordance with the principle of operation and the characteristics of a sensor is required and further design know-how specific to analog is needed, and therefore a dedicated AFE circuit or a dedicated IC has been developed for a specific sensor by narrowing down the principle of operation and the characteristics of a sensor to serve as a target.
An AFE circuit according to related art is disclosed in Japanese Unexamined Patent Application Publication No. 10-320684, for example. FIG. 55 shows the circuit configuration according to the related art disclosed therein. The circuit includes a sensor 903, an analog input circuit 911, which is an analog front-end circuit, and a microcomputer 910.
The analog input circuit 911 includes a transformer 920 that receives a signal from the sensor 903, a filter 921 that allows a signal component with a specific frequency to pass through, an amplification circuit 922 that amplifies the output of the filter 921, an A/D converter 923 that converts the output of the amplification circuit 922 from analog to digital, and a comparator circuit 924 that compares the output of the amplification circuit 922 with a reference voltage.
The microcomputer 910 processes a digital signal that is output from the A/D converter 923 and performs processing in accordance with the detection of the sensor 903. Further, the microcomputer 910 outputs a control signal to the filter 921 and changes the frequency characteristics of the filter 921.